1. Field of the Invention
This invention relates to gas generators for inflating vehicle inflatable restraint cushions, commonly known as air or gas bags, to provide impact protection to occupants of the vehicles.
2. Description of the Prior Art
The gas bag is located forward of the occupants and normally is in a deflated condition. In the event of a crash, however, the gas bag is inflated in a matter of a few milliseconds by a gas produced by the burning of a gas generant material in an inflator. The gas generant is ignited by an igniter. The pressure of combustion gases resulting from the rapid burning of the gas generant material causes gas to rush into the bag to effect a rapid rate of inflation thereof.
An out of place child standing in close proximity to a gas bag compartment of an automobile could be injured if all of the gas pressure were released into the bag instantaneously. In order to preclude the possibility of such injury, the bag should initially deploy slowly to gently push the child away. Then, after an appropriate delay, an interval of twenty milliseconds, for example, the bag may be allowed to expand rapidly to protect all passenger seat occupants. A graph of pressure vs. time performance that will produce such an initially gentle but firm gas bag inflating action followed immediately by rapid gas bag inflation is commonly known as an S-curve. Such a curve is illustrated in each of FIGS. 1 and 5.
Several proposals have been made in the prior art to accomplish such performance. In order to establish S-curve parameters, it has been proposed to use a so-called two-stage inflator.
In one such prior art proposal, two driver side inflators are arranged to deploy into a single passenger side gas bag with a time delay between initiation of the initiator of a second one of the inflators after the initiator of a first one thereof has been initiated.
Other proposals have involved two-stage inflators comprising a single inflator housing that has been divided into two chambers or compartments each of which contain combustible gas generant material, and which may be of unequal size. Because a smaller amount of gas is required from the chamber that is first to be ignited, that chamber may be the smaller of the two chambers. When deploying the gas bag, the gas generant material in the first or smaller chamber is ignited, and after some delay, the gas generant material in the second or larger chamber is ignited. Several methods have been proposed for achieving such ignition delay.
As disclosed in U.S. Pat. No. 3,663,035 to Norton, each chamber of a two chamber or two-stage inflator is mounted at one end of a block containing an ignition cavity. This ignition cavity is common to both chambers. A fixed delay line separates one of the chambers from the ignition cavity and delays ignition of that chamber by a few milliseconds.
In U.S. Pat. No. 3,972,545 to Kirchoff et al., which patent is assigned to the assignee of the present invention, a consumable partition is provided in an inflator. The partition divides the inflator into two chambers each of which contains gas generant material that is ignitable by an individually associated initiator or squib. An impact sensor determines whether one or both of the squibs is initiated or fired on collision impact, depending upon the force of the collision, and thus the rate at which the gas bag is to be filled with gas. That is to say, if the impact is less severe, only the first or downstream squib will be fired. In such case combustion proceeds upstream through the consumable partition to fire the squib and the gas generant material in the upstream chamber, thereby to provide a slower rate of inflation for a softer cushioning effect.
U.S. Pat. No. 4,213,635 to Inokuchi et al. discloses an inflator having two gas generating chambers that are separated by a dividing wall. An individually associated igniter is provided for each chamber. Ignition of the igniter in the second chamber is delayed by a signal generator in the first chamber that detects the level of gas pressure therein. When the pressure level reaches a predetermined value, the igniter in the second chamber is ignited.
In U.S. Pat. No. 4,358,998 to Schneiter et al., which patent is assigned to the assignee of the present invention, there is disclosed an igniter assembly for an inflator that is operable to cause the combustible gas generant material in a single combustion chamber to ignite in a progressive manner so as to effect inflation of the gas bag slowly initially but more rapidly later as inflation progresses. The igniter assembly includes a solid propellant disc between two portions thereof whereby the gas generant material disposed around one portion is ignited immediately, and then, after burn through of the disc, the gas generant material disposed around the other portion is ignited. The time required to burn through the disc is the delay time.
Pending U.S. applications for patent bearing application Ser. No. 310,122, filed Feb. 10, 1989 and application Ser. No. 372,994 filed June 29, 1989 by Lauritzen and Ward, which applications are assigned to the assignee of the present invention, each disclose a gas bag inflator comprising an elongated extruded housing having an extruded portion with an intermediate imperforate bulkhead integral with the tubular portion whereby there is provided two isolated chambers. Combustible gas generant means is included in each chamber as is also an individually associated squib. Tailoring of the inflator to the specific needs of a vehicle at the time of a crash may be effected by cutting each end to size after the housing is extruded. The chambers may be provided with different gas generating materials for a softer onset of inflation of the gas bag. Also, some of the common input parameters such as speed and ambient temperature that are monitored by microprocessors in common use in vehicles may be employed to determine the correct time delay in the firing of the individually associated squib in each of the chambers.
A continuation-in-part of U.S. application Ser. No. 310,122 bearing application Ser. No. 409,456, filed on Sept. 22, 1989 by Lauritzen and Ward, and assigned to the assignee of the present invention, contains a similar disclosure.
The foregoing proposals for providing more controlled gas bag inflation that is tailored to the needs of the occupants of a vehicle at the time of a crash have advanced the state of the art. There is, however, a need and a demand for further improvement in reducing the complexity of the inflator ignition delay system, the number of failure modes of the inflator, and the cost of inflator fabrication.